1. Field of the Invention
The present invention relates to a calibration system for disc drives, and in particular to a calibration system using an on-screen display module to calibrate the inclined angle of the pick-up module in disc drives.
2. Description of the Related Art
Pick-up modules are one of the key components in conventional disc drives, such as DVD-ROMs or CD-ROMs. However, when assembling a disc drive, the optical axis of the pick-up module must be parallel, or have a predetermined included angle, relative to the normal angle of an inserted disc, ensuring that the pick-up module can function properly. Thus, conventional disc drives usually have tilt-adjusting mechanisms to calibrate the optical axis of pick-up modules.
FIG. 1 is a perspective view of a conventional disc drive. In FIG. 1, the disc drive has a pick-up module 11 driven by a sliding mechanism 12, a stage 13 driven by a spindle motor and a control PCB 14. The sliding mechanism 12 includes two lead screws 15 arranged in parallel, forming a surface on which the pick-up module 11 moves. The height of one end of a major lead screw can be adjusted, and the other end is fixed. Furthermore, the height of both ends of the other lead screw can be adjusted, such that the sliding surface of the pick-up module 11 can be modified. When a disc is loaded, it is possible that the disc and the sliding surface are not parallel because of the inaccuracy of the spindle motor, or the improper assembly of the lead screws 15. It can cause jitters of 10 μm˜1 mm during disc rotation. Thus, the data received by the pick-up module 11 may have errors.
A conventional calibration method includes two steps. First, the inclined angle and vibration of the disc supported by the stage is adjusted through an autocollimator. Next, the jitter value of RF signals emitted by the pick-up module is tuned through a jitter meter. The jitter value must be lower than a predetermined value to ensure the accuracy of output data. Unqualified disc drives with a jitter value higher than the predetermined value will again be adjusted.
Jitter meters used in the conventional calibration method are easily jammed by external noise. They cannot directly determine the optimum jitter value of each pick-up module, and each pick-up module must be checked several times to ensure product quality.
Moreover, because the reading light paths for CDs and DVDs are different, the jitter values with respect to CDs or DVDs of the same pick-up module are different. Thus, the conventional calibration method individually calibrates the jitter value of CDs and DVDs, thus complicating fabrication. Additionally, the inclined angle of the sliding surface and the jitter value cannot be simultaneously calibrated. Hence, there is a need for a better calibration system, which addresses this problem, and simplifies the conventional calibration method.